1. Field of the Invention
The present invention relates to a feedforward amplifier circuitry and, in particular the present invention relates to a feedforward amplifier circuitry capable of removing or eliminating a distortion component of an amplifier by using predistortion compensating mean.
2. Description of the Related Art
FIGS. 9 and 10 illustrate block circuit diagrams showing feedforward amplifier circuitries as disclosed in Japanese Patent No. 3106996.
Referring to FIG. 9, an input signal from an input terminal 1 is distributed via a distributor 2 to signal paths a and b. The signal outputted on the signal path a passes through a predistortion circuit 3, a variable attenuator 4 and a variable phase shifter 5 and then receives an injection of a pilot signal generated from a pilot signal generator 16, thereafter inputted into a main amplifier 6. As is clear from FIG. 9, the variable attenuator 4 and the variable phase shifter 5 are controlled by a control circuit 19.
Subsequently, an output from the main amplifier 6 is inputted into a distributor 7 one distributed output of which is fed through a delay line 8 to a combiner 9 and the other distributed output of which is fed to a combiner 11. The combiner 11 combines a signal passed through a delay line 10 with an output from the distributor 7. An output of the combiner 11 passes through a variable attenuator 12 and a variable phase shifter 13, thereafter inputted into an auxiliary amplifier 14. As is clear from FIG. 9, the variable attenuator 12 and the variable phase shifter 13 is controlled by the control circuit 19.
An output from the auxiliary amplifier 14 is combined with a signal passed through the delay 8 by the combiner 9, thereafter outputted from an output terminal 15. From an output point of the combiner 11, a carrier component (which is a single frequency component of a signal to be fed into the input terminal 1 and to be amplified) is detected and then a level of its detected carrier component is inputted into the control circuit 19. Also, from an output point of the combiner 9, a level of the pilot signal which has been injected into an output from the variable phase shifter 5 is detected by a pilot signal detector 18, thereafter inputted into the control circuit 19. On the other hand, between the combiner 11 and the variable attenuator 12 in a feedforward amplifier circuitry as shown in FIG. 10 is provided a predistortion circuit 20.
In each of the feedforward amplifier circuitries as shown in FIGS. 9 and 10, the main amplifier 6 and the auxiliary amplifier 14 change in operating point dependently on their temperature characteristics in accordance with an ambient temperature variation, as a result of which each of the feedforward amplifier circuitries can disadvantageously shift its optimal point for eliminating or removing a distortion as a whole.
Thus, the applicant proposes a feedforward amplifier circuit having a predistortion temperature compensating circuit 21 arranged therein as shown in FIGS. 11 and 12 and which has already been filed as Japanese Patent Application HEI-2001-281906.
The feedforward amplifier circuitries as shown in FIGS. 11 and 12 are substantially similar to those as shown in FIGS. 9 and 10, but distinguish from the latter in that the predistortion temperature compensating circuits 21 are provided for the predistortion circuits 3, respectively.
The feedforward amplifier circuits as shown in FIGS. 11 and 12 exhibit good performances without shifting in optimal point for eliminating distortions in accordance with the ambient temperature. However, the fact which is common to both of the feedforward amplifier circuitries as shown in FIGS. 9 to 12 is that, upon implementation of actual circuit composition for such a feedforward amplifier circuit on a circuit board, a problem rises such that there is present lack of flexibility in terms of a location (or placement) of each section which partially configures the feedforward circuitry without any reverse influence on the completed feedforward amplifier circuit.
The present invention aims to solve or at least reduce this problem. It is, therefore, an object of the present invention to provide a feedforward amplifier circuitry which is capable of changing a location of each section which partially configures the feedforward circuitry and, in particular, a feedforward amplifier circuitry which is capable of changing an interposing location of a variable phase shifter.
According to an aspect of the present invention, there is provided a feedforward amplifier circuitry comprising:
a distortion detecting means for detecting a distortion component in an output signal of an amplifier;
a distortion eliminating means for eliminating the distortion component in the output of said amplifier by subtracting a signal based on the distortion component detected by said distortion detecting means from the output signal of said amplifier;
a pre-stage distortion compensating means disposed at least on either one side of said distortion detecting means and said distortion eliminating means and generating a distortion component to be eliminated as the distortion component of said amplifier; and
a variable phase shifter means disposed at least on either one side of said distortion detecting means and said distortion eliminating means,
wherein said variable phase shifter means disposed on either one side of said distortion detecting means and said distortion eliminating means, if said pre-stage distortion compensating means is disposed on either one side thereof, is disposed on a location other than a post-stage of said pre-stage distortion compensating means.
Thus, the feedforward amplifier circuitry according to the present invention allows the variable phase shifter to be disposed on an appropriate location. Therefore, it is possible to provide a designer with more flexibility in changing a location or placement of the variable phase shifter, regardless of the conventional arrangement of the variable phase shifter disposed on the post-stage of the distortion circuit when the feedforward amplifier is actually designed, without any reverse influence on the feedforward amplifier circuit.
According to another aspect of the present invention, there is further provided a feedforward amplifier circuitry comprising:
a distortion detecting means for detecting a distortion component in an output signal of an amplifier;
a distortion eliminating means for eliminating the distortion component in the output of said amplifier by subtracting a signal based on the distortion component detected by said distortion detecting means from the output signal of said amplifier;
a pre-stage distortion compensating means disposed at least on either one side of said distortion detecting means and said distortion eliminating means and generating a distortion component to be eliminated as the distortion component of said amplifier;
temperature compensating means for adding a temperature compensation function to said pre-stage distortion compensating means such that the distortion component generated by said pre-stage distortion compensating means is optimized according to an ambient temperature; and
a variable phase shifter means disposed at least on either one side of said distortion detecting means and said distortion eliminating means,
wherein said variable phase shifter means disposed on either one side of said distortion detecting means and said distortion eliminating means, if said pre-stage distortion compensating means is disposed on either one side thereof, is disposed on a location other than a post-stage of said pre-stage distortion compensating means.
Thus, the feedforward amplifier circuitry according to the present invention allows not only the variable phase shifter to be disposed on an appropriate location, but also the pre-stage distortion compensating means to be optimally controlled for eliminating the distortion component in the output signal of the amplifier by means of the temperature compensation function of the temperature compensating means. Similarly to the above configuration of the feedforward amplifier circuitry, it is also possible to provide a designer with more flexibility in changing a location or placement of the variable phase shifter, regardless of the conventional arrangement of the variable phase shifter disposed on the post-stage of the distortion circuit when the feedforward amplifier is actually designed, without any reverse influence on the feedforward amplifier circuit.
These and other aspects of the present invention will be apparent from the following specific description, given by way of example, with reference to the accompanying drawings.